Synthetic studies towards the tunicamycins and analogues based on diazo chemistry. Total synthesis of tunicaminyl uracil

A synthetic approach to the tunicamycins, a complex family of nucleosides with potent antibiotic and antiviral activities is reported based on diazo chemistry. The corresponding precursors for the synthesis of tunicaminyl uracil derivatives, the non-stabilized diazo derived from 13 and the aldehyde derivative of uridine, compound 4, were prepared efficiently from commercially available D-galactal and uridine, respectively. After a high yielding coupling reaction to obtain the ketone 14, a stereoselective reduction provided the corresponding tunicaminyl uracil derivative 17a and its C-7 epimer 17b. The interconversion of the diazo and aldehyde functional groups in the requisite building blocks was similarly achieved to obtain the ketone 32, which after reduction yielded the corresponding 7-deoxy-6-hydroxy tunicaminyl uracil analogs 33a and 33b.     

Photochemistry of 2-(1-naphthyl)-2H-azirines in matrixes and in solutions: wavelength-dependent C-C and C-N bond cleavage of the azirine ring

The photochemistry of 3-methyl-2-(1-naphthyl)-2H-azirine (1a) was investigated by the direct observation of reactive intermediates in matrixes at 10 K and by the characterization of reaction products in solutions. As already reported, the photolysis of the azirine 1a with the short-wavelength light (>300 nm) caused the C-C bond cleavage of the 2H-azirine ring to produce the nitrile ylide 2. However, the products derived from the C-N bond cleavage were exclusively obtained in the irradiation of 1a with the long-wavelength light (366 nm) both in matrixes and in solutions. When 1a was irradiated in the presence of O(2) with the long-wavelength light, acetonitrile oxide (6) was produced through the capture of the biradical 4 generated by the C-N bond cleavage of 1a with O(2). An introduction of a nitro group into the naphthyl ring of 1a resulted in an acceleration of the decomposition in the long-wavelength irradiation and an extension of the wavelength region where the products derived from the C-N bond cleavage were selectively obtained. On the basis of molecular orbital calculations with the INDO/S method, the reason for the wavelength-dependent selective C-C and C-N bond cleavage of the azirine ring of 1a is discussed.     

Experimental and theoretical investigation of reversible interconversion, thermal reactions, and wavelength-dependent photochemistry of diazo Meldrum's acid and its diazirine isomer, 6,6-dimethyl-5,7-dioxa-1,2-diaza-spiro[2,5]oct-1-ene-4,8-dione

The photochemical or thermal decomposition of diazo Meldrum's acid (1) in methanolic solutions yields ketoester 3a, the product of the Wolff rearrangement, while products produced from the singlet carbene were not detected. This observation, combined with the analysis of activation parameters for the thermal decomposition of 1, as well as with the results of DFT B3PW91/6-311+G(3df,2p) and MP2/aug-cc-pVTZ//B3PW91/6-311+G(3df,2p) calculations, allows us to conclude that the Wolff rearrangement of 1 is a concerted process. The outcome of the photolysis of diazo Meldrum's acid depends on the wavelength of irradiation. Irradiation with 254 nm light results in an efficient (Phi(254) = 0.34) photo-Wolff reaction, while at 355 nm, the formation of diazirine 2 becomes the predominant process (Phi(350) = 0.024). This unusual wavelength selectivity indicates that Wolff rearrangement and isomerization originate from different electronically excited states of 1. The UV irradiation of diazirine 2 leads to the loss of nitrogen and the Wolff rearrangement, apparently via a carbene intermediate. This process is accompanied by a reverse isomerization to diazo Meldrum's acid. Triplet-sensitized photolysis of both isomers results in the formation of Meldrum's acid, the product of a formal reduction of 1 and 2. Mild heating of diazirine 2 produces quantitative yields of diazo Meldrum's acid. The activation parameters for thermal reactions of diazo 1 and diazirino 2 isomers were determined in aqueous and dioxane solutions.     

Design,Synthesis of N-benzoyloxy-thiono-1,8-naphthalimides as Novel DNA Photocleavers

In recent years, It is of great interest to the design and synthesis of DNA photocleaving reagents that can generate active species by long-wavelength UV-light (λ>350nm) or more preferably by visible light irradiation. Our studies are based upon 1,8-naphthalimide-derivitives, which usually exhibit strong visible absorption and good DNA intercalative binding abilities.     

Wavelength-dependent photochemistry of Diazo Meldrum's acid and its spirocyclic isomer,Diazirino Meldrum's acid: Wolff rearrangement versus isomerization

Photoreaction of diazo Meldrum's acid (1) shows a unique wavelength selectivity. At 254 nm it results in efficient (phi(254) = 0.34) Wolff rearrangement, while irradiation with 355 nm light leads to a completely different process, isomerization into corresponding cyclic alpha,alpha"-dicarbonyl diazirine 2 (phi(350) = 0.024). UV photolysis of diazirine 2 is accompanied by two competing processes: loss of nitrogen followed by the Wolff rearrangement and isomerization into diazo compound 1. Thermal decomposition of 1 leads to clean Wolff rearrangement, while heating of 2 causes quantitative conversion into diazo isomer 1.     

Photochemistry and Reactivity of the Phenyl Radical–Water System: A Matrix Isolation and Computational Study

The reaction of the phenyl radical 1 with water has been investigated by using matrix isolation spectroscopy and quantum chemical calculations. The primary thermal product of the reaction between 1 and water is a weakly bound complex stabilized by an OH???π interaction. This complex is photolabile, and visible‐light irradiation (λ>420 nm) results in hydrogen atom transfer from water to radical 1 and the formation of a highly labile complex between benzene and the OH radical. This complex is stable under the conditions of matrix isolation, however, continuous irradiation with λ>420 nm light results in the complete destruction of the aromatic system and formation of an acylic unsaturated ketene. The mechanisms of all reaction steps are discussed in the light of ab initio and DFT calculations.     

Early events in the photochemistry of 2-naphthyl azide from femtosecond UV/Vis spectroscopy and quantum chemical calculations: direct observation of a very short-lived singlet nitrene

Exposure of 2-naphthyl azide in acetonitrile at ambient temperature to femtosecond pulses of 266 nm light produces a transient absorption with maxima at 350 and 420 nm. The carrier of the 350 nm band decays more rapidly than that of the 420 nm band which has a lifetime of 1.8 ps. Analogous experiments with 1-chloro-2-naphthyl azide in methanol allow the assignment of the 350 nm band to a singlet excited state of 2-naphthyl azide and the carrier of the 420 nm band to singlet 2-naphthylnitrene. This reactive intermediate has the shortest lifetime of any singlet nitrene observed to date and is a true reactive intermediate. Computational studies at the RI-CC2 level of theory support these conclusions and suggest that initial excitation populates the S2 state of 2-naphthyl azide. The S2 state, best characterized as a pi --> (pi*, aryl) transition, has a geometry similar to S0. S2 of 2-naphthyl azide can then populate the S1 state, a pi --> (in-plane, pi*, azide) excitation, and in the S1 state, electron density is depleted along the proximal N-N bond. S1 is dissociative along that N-N coordinate to form the singlet nitrene, and with a barrier of only approximately 5 kcal/mol for N2 extrusion.     

UV-induced oxo --> hydroxy unimolecular proton-transfer reactions in hypoxanthine

Monomers of hypoxanthine isolated in low-temperature Ar matrixes were studied using Fourier transform infrared spectroscopy. Two most stable tautomeric forms of hypoxanthine: oxo-N(9)-H and oxo-N(7)-H as well as a very small amount of the minor hydroxy-N(9)-H tautomer were observed in Ar matrixes directly after their deposition. UV irradiation of the matrixes induced conversion of the oxo-N(9)-H and oxo-N(7)-H tautomers of the compound into the hydroxy-N(9)-H and hydroxy-N(7)-H forms, respectively. Upon exposure of the matrixes to the UV (lambda > 270 nm) light, the oxo-N(9)-H --> hydroxy-N(9)-H phototautomeric reaction dominated strongly over the oxo-N(7)-H --> hydroxy-N(7)-H phototransformation. The latter phototautomeric reaction occurred effectively when matrix-isolated hypoxanthine was irradiated with shorter-wavelength (lambda > 230 nm) UV light. Thanks to this wavelength dependency, it was possible to clearly distinguish the oxo --> hydroxy photoreaction within the N(9)-H tautomers from the analogous phototautomeric process within the N(7)-H tautomers. All of the observed isomers of hypoxanthine (substrates and products of the photoreactions) were identified by comparison of their IR spectra with the spectra calculated at the DFT(B3LYP)/6-31++G(d,p) level of theory.     

Structure,Spectra and Photochemistry of 2-Amino-4-Methylthiazole: FTIR Matrix Isolation and Theoretical Studies

The structure, tautomerization pathways, vibrational spectra, and photochemistry of 2-amino-4-methylthiazole (AMT) molecule were studied by matrix isolation FTIR spectroscopy and DFT calculations undertaken at the B3LYP/6-311++G(3df,3pd) level of theory. The most stable tautomer with the five-membered ring stabilized by two double C=C and C=N bonds, was detected in argon matrices after deposition. When the AMT/Ar matrices were exposed to 265 nm selective irradiation, three main photoproducts, N-(1-sulfanylprop-1-en-2-yl)carbodiimide (fp1), N-(1-thioxopropan-2-yl)carbodiimide (fp2) and N-(2-methylthiiran-2-yl)carbodiimide (fp3), were photoproduced by a cleavage of the CS–CN bond together with hydrogen atom migration. The minor photoreaction caused by the cleavage of the CS–CC bond and followed by hydrogen migration formed 2-methyl-1H-azirene-1-carbimidothioic acid (fp15). We have also found that cleavage of the CS–CN bond followed by disruption of the N–C bond produced cyanamide (fp11) and the C(CH3)=CH–S biradical that transformed into 2-methylthiirene (fp12) and further photoreactions produced 1-propyne-1-thiole (fp13) or methylthioketene (fp14). Cleavage of the CS–CC bond followed by disruption of the N–C bond produced propyne (fp22) and the S–C(NH₂)=N biradical that transformed into 3-aminethiazirene (fp23); further photoreactions produced N-sulfanylcarbodiimide (fp25). As a result of these transformations, several molecular complexes were identified as photoproducts besides new molecules in the AMT photolysis process.     

UV-Induced unimolecular photochemistry of diketene isolated in cryogenic inert matrices

Diketene (C(4)H(4)O(2)) monomers were isolated in cryogenic Ar (15 K) and Xe (30 K) matrices. The infrared (IR) spectra of the freshly deposited matrices show that diketene monomers exclusively adopt the 4-methylene-oxetan-2-one form. In situ photochemical transformations of diketene were induced by tunable UV laser light. Diketene was found to be photostable when exposed to near-UV irradiations (λ> 300 nm). Irradiations in the middle-UV domain showed different types of photochemical reactivity occurring upon irradiations with 280 > λ > 240 nm and λ = 225 nm. The photoproducts were characterized by IR spectroscopy supported by B3LYP/6-311++G(d,p) calculations. Upon irradiation in the 280 > λ > 225 nm range, diketene was found to decompose in two ways: (i) with production of two parent ketene molecules (O═C═CH(2)), and (ii) with production of cyclopropanone (CP) plus carbon monoxide. For irradiations in the 280 > λ > 240 nm range, diketene exhibited two additional reactions: (iii) decomposition to allene (H(2)C═C═CH(2)) and carbon dioxide, and (iv) isomerization into cyclobutane-1,3-dione (CB). Of the above photoproducts, CP and CB were consumed by the same UV irradiations that resulted in their generation. Positive spectroscopic identification of CP and CB turned out to be possible with near-UV irradiations: CP decomposes to ethylene and carbon monoxide upon irradiation with λ = 345 nm; CB decomposes exclusively to two parent ketene molecules, without isomerization back to diketene or decarbonylation, upon irradiation with λ = 330 nm. Natural bond orbital (NBO) analysis showed that the two lowest excited singlet states of diketene are almost degenerate in energy and correspond to π* orbitals of C═C and C═O moieties. The NBO calculations helped to establish that the third excited singlet state, in terms of energy, has σ*(3s) Rydberg character, in accord with the literature.     

On the photochemical conversion of an alpha, beta-unsaturated gamma, delta-epoxy ketone: 3-oxo-6-alpha, 7-alpha-oxide-17-beta-acetoxy-Delta-androstane

The α,β-unsaturated γ,δ-epoxyketone 7 is isomerized almost exclusively to the δ-diketone 9 both upon irradiation in the n → π* absorption band with light of wavelengths above 310 nm (in anhydrous dioxane or benzene solutions) and upon triplet sensitization using acetophenone in benzene. The reaction may be formulated by the cleavage of the C_γ? O oxide bond and the shift of the δ-hydrogen to the γ-position, and thus bears a formal “double bond homology” to the photochemical α,β-epoxyketone rearrangement. Excitation in the π → π* absorption band of 7 with light of wavelength 253,7 nm (in anhydrous dioxane solution) leads to the formation of product 10 as well as to the triplet rearrangement to 9 . With this result a novel partial synthesis of O-acetyl-B-nortestosterone has been accomplished, which has the advantages of fewer steps and higher product yield ( 7 → 10 : ～30% yield) than previously published syntheses. On the basis of the presently available experiments, the mechanism of the transformation 7 → 10 , which constitutes one of the still few examples of enone photoreactions induced selectively from the π,π* excited singlet, remains unknown.     

Photochemie von tricyclischen β, γ-γ′, δ′-ungesättigten Ketonen. 50. Mitteilung über Photoreaktionen

Photochemistry of tricyclic β, γ-γ′, δ′-unsaturated ketones The easily available tricyclic ketone 1 (cf. Scheme 1) with a homotwistane skeleton yielded upon direct irradiation the cyclobutanone derivative 3 by a 1,3-acyl shift. Further irradiation converted 3 into the tricyclic hydrocarbon 4 . However, acetone sensitized irradiation of 1 gave the tetracyclic ketone 5 by an oxa-di-π-methane rearrangement. Again with acetone as a sensitizer the ketone 5 was quantitatively converted to the pentacyclic ketone 6 . The conversion 5 → 6 represents a novel photochemical 1,4-acyl shift. The possible mechanisms are discussed (see Scheme 7). The tricyclic ketone 2 underwent similar types of photoreactions as 1 (Scheme 2). Unlike 5 the tetracyclic ketone 9 did not undergo a photochemical 1,4-acyl shift. The epoxides 10 and 14 derived from the ketones 1 and 2 , respectively, underwent a 1,3-acyl shift upon irradiation followed by decarbonylation, and the oxa-di-π-methane rearrangement (Schemes 3 and 4). The diketone 18 derived from 1 behaved in the same way (Scheme 5). The tetracyclic diketone 21 cyclized very easily to the internal aldol product 22 under the influence of traces of base (Scheme 5). Upon irradiation the γ, δ-unsaturated ketone 24 underwent only the Norrish type I cleavage to yield the aldehyde 25 (Scheme 6).     

Photolysis of 6-ethoxy-2,2,4-trimethyl-8-nitro-1,2-dihydroquinoline. Unusual dependence on the irradiation wavelength

The spectral and kinetic parameters of transient species generated in the irradiation of 6-ethoxy-2,2,4-trimethyl-8-nitro-1,2-dihydroquinoline were examined by stationary and pulse photolysis in the solvents: heptane, acetonitrile, methanol, and ethanol. Upon excitation of the long-wavelength absorption band (λ_ex > 450 nm), a reversible photochemical reaction was revealed, and the spectral and kinetic parameters of three transient species observed in the photolysis were characterized (λ_max = 390, 400, and 420 nm (acetonitrile), k = 97, 500, and 2000 s⁻¹, respectively). The absorption spectra and the rate constants of the decay of transient species are almost independent of the medium polarity and the presence of oxygen in the system. The excited state generated during irradiation to the short-wavelength absorption band (290 < λ_ex < 350 nm) is inactive in the photochemical reaction and deactivates without the formation of transient species. The mechanism of the reversible photochemical reaction is suggested, which involves the opening of the heterocycle N-C bond upon photoexcitation of the long-wavelength absorption band and the thermal back reaction.     

Masked Rhodamine Dyes of Five Principal Colors Revealed by Photolysis of a 2‐Diazo‐1‐Indanone Caging Group: Synthesis,Photophysics, and Light Microscopy Applications

Caged rhodamine dyes (Rhodamines NN) of five basic colors were synthesized and used as “hidden” markers in subdiffractional and conventional light microscopy. These masked fluorophores with a 2‐diazo‐1‐indanone group can be irreversibly photoactivated, either by irradiation with UV‐ or violet light (one‐photon process), or by exposure to intense red light (λ～750 nm; two‐photon mode). All dyes possess a very small 2‐diazoketone caging group incorporated into the 2‐diazo‐1‐indanone residue with a quaternary carbon atom (C‐3) and a spiro‐9H‐xanthene fragment. Initially they are non‐colored (pale yellow), non‐fluorescent, and absorb at λ=330–350 nm (molar extinction coefficient (ε)≈10⁴ M^?1 cm^?1) with a band edge that extends to about λ=440 nm. The absorption and emission bands of the uncaged derivatives are tunable over a wide range (λ=511–633 and 525–653 nm, respectively). The unmasked dyes are highly colored and fluorescent (ε= 3–8×10⁴ M^?1 cm^?1 and fluorescence quantum yields (?)=40–85 % in the unbound state and in methanol). By stepwise and orthogonal protection of carboxylic and sulfonic acid groups a highly water‐soluble caged red‐emitting dye with two sulfonic acid residues was prepared. Rhodamines NN were decorated with amino‐reactive N‐hydroxysuccinimidyl ester groups, applied in aqueous buffers, easily conjugated with proteins, and readily photoactivated (uncaged) with λ=375–420 nm light or intense red light (λ=775 nm). Protein conjugates with optimal degrees of labeling (3–6) were prepared and uncaged with λ=405 nm light in aqueous buffer solutions (?=20–38 %). The photochemical cleavage of the masking group generates only molecular nitrogen. Some 10–40 % of the non‐fluorescent (dark) byproducts are also formed. However, they have low absorbance and do not quench the fluorescence of the uncaged dyes. Photoactivation of the individual molecules of Rhodamines NN (e.g., due to reversible or irreversible transition to a “dark” non‐emitting state or photobleaching) provides multicolor images with subdiffractional optical resolution. The applicability of these novel caged fluorophores in super‐resolution optical microscopy is exemplified.     

Noncommunicating photoreaction paths in some pregna-1,4-diene-3,20-diones.

The photochemistry of three pregna-1,4-diene-3,20-diones bearing a hydroxy or alkoxy group at C(17) (4-6) has been examined. Irradiation at 254 or 366 nm, where absorption by the cross-conjugated ketone moiety in ring A is predominant or exclusive, causes the 'lumiketone' rearrangement of this chromophore in low to medium quantum yield (Phi(r) 0.05 to 0.31). On the contrary, irradiation at 310 nm, where the isolated ketone at C(20) absorbs a large portion of light causes Norrish-I fragmentation of that chromophore with a higher Phi(r) (0.11-0.83). This leads to end-products arising from the conversion of the C(17) alkyl radical, in a way depending on the structure and the medium (reduction by hydrogen donating solvent, addition of oxygen when present). No intramolecular T-T energy transfer between the separated chromophores occurs. The 'lumiketone' rearrangement occurs independently from the irradiation wavelength (Phi(r) 0.06-0.18) with the strictly related androsta-1,4-dien-3-one 8 lacking the C(20) ketone function.     

Photochemical and Photophysical Studies of 3-Amino-6-lodoacridine and the Inactivation of λ Phage

Abstract— The photochemistry and photophysics of 3-amino-6-io-doacridine (Acr-I) was studied. Photolysis (350 nm) of Acr-I (free base) generates products consistent with a free radical intermediate in methanol, benzene and carbon tetrachloride. The Acr-I hydrochloride is shown to bind to calf thymus DNA and to the self-complementary dinucleotide cytidylyl-(3′-5′)-guanosine (CpG) minidu-plex in a manner similar to that of proflavine (Acr-NH₂), a known DNA intercalator. The Acr-I is shown to more efficiently nick supercoiled plasmid DNA pBR322 upon 350 nm or 420 nm photolysis than Acr-NH₂. The efficiency of Acr-I-sensitized DNA nicking is not oxygen dependent. Photolysis of the Acr-I/(CpG)₂ complex leads to cleavage of the dinucleotide and to cytidine base release by selective damage to a specific ribose moiety. Dinucleotide cleavage occurs equally well in the presence or absence of oxygen, thereby eliminating a singlet oxygen- or peroxyl radical-mediated process. Photolysis of Acr-I in the presence of a mononucleotide (GMP) or a non-self-complementary dinucleotide (uridylyl-[3′-5′]-cytidine– UpC) does not lead to fragmentation and base release. Similarly, photolysis of the Acr-NH₂/(CpG)₂ complex does not lead to fragmentation and base release. The data indicate that photolysis of an iodinated intercalator bound to CpG or plasmid DNA generates an intercalated aryl radical and that the reactive intermediate initiates a sequence of reactions that efficiently nick nucleic acids. The inactivation of Λ phage sensitized by Acr-I with UV (350 nm) light is oxygen independent but with visible (420 nm) light is strongly oxygen dependent. The Acr-I fluoresces more intensely when excited at 446 than at 376 nm. Thus, UV photolysis may lead to C-I bond homolysis and free radical formation, a process that is not energetically feasible with visible light. The results demonstrate the difficulty of extrapolating model studies involving simple molecules and DNA to understanding the mechanism of viral inactivation with a particular sensitizer.     

Photochemische Reaktionen. 106. Mitteilung. Zur Photochemie tetraalkylsubstituierter γ-Keto-olefine

The Photochemistry of Tetraalkyl Substituted γ-Keto-olefines The photochemistry of 7,8-dihydro-β-ionone ( 1 ) in solution is shown to depend on temperature, polarity and viscosity of the solvent. UV. irradiation (λ ≥ 245 nm) in pentane at +25° converts 1 to the isomeric ethers 3 (16%), 5A (48%) and 5B (22%), whereas at ?65° 7,8-dihydro-γ-ionone ( 26 ) is obtained in 12% yield together with 13% of 3 , 12% of 5A and 9% of 5B . The ¹n,π*-excitation of 1 in acetonitrile gives similar results. In the more viscous 1,2,3-triacetoxypropane the photoisomerization 1 → 26 takes place even at + 60° (10% yield, cf. 40% at ?15°). In alcoholic solvents, however, no formation of 26 is detected, but the hitherto unknown [2+2]-photocycloaddition 1 → 11 can be observed (4% at ?7°, 15% at ?65S° in 2-propanol). An intermediate e may be involved (Scheme 14). In addition to the photoreactions 1 → 3, 5A, 5B and 11 the isomerization of 1 to the novel spirocyclic ketone 28 takes place in alcoholic solvents only. Photoisomerization 1 → 3 is presumably a photo-ene process involving a stereoselective intramolecular H-transfer. This type of photoisomerization is restricted to cyclic γ-keto-olefines. The tetraalkylated acyclic γ-keto-olefines 14 and 15 photoisomerize exclusively by [2+2]-cycloaddition, independent of the solvent. On ¹n,π*-excitation the δ,?-unsaturated bicyclic ketone 44 undergoes Norrish-Type-II photofragmentation to the diene 45 or isomerizes to the γ, ?-unsaturated ketone 17 . Competition between these two reactions is strongly temperature dependent: photolysis in pentane at ?72° yields quantitatively 45 , whereas at + 35° only 30% of 45 and 68% of 17 are obtained. UV. irradiation of the novel spirocyclic ketone 28 gives as primary photoproduct the isomeric aldehyde 29 , and in a secondary photoreaction the isomeric oxetanes 30A and 30B . Experiments with deuteriated substrates show that the isomerization of type 28 → 29 is stereocontrolled.     

Photochemisches Verhalten von N-Acyl-11-methyl-hexahydrocarbazolen

The irradiation of N-acylated 11-methyl-1,2,3,4,10,11-hexahydrocarbazoles (compounds 6–10 ) and of the 8-methoxy derivatives 11–13 in hexane solution, with 254 nm light, in the presence of air, leads to 11-methyl-2,3,4,11-tetrahydro-1 H-carbazole ( 2 ) (table 1) and its 8-methoxy derivative 21 , respectively (scheme 2). Furthermore the 8-acylated products. 14, 15, 16, 18 , are formed in minor amounts by a “photoanilide” rearrangement. Irradiation of the N-acetyl-8-methoxy-indoline 12 gives in addition (by elimination of the 8-methoxy group) the 8-acetyl-indoline 14 and, by coupling, the dimeric compound 23 (schemes 2 and 4). Irradiation of the N-formyl-indoline 6 yields, besides the indolenine 2 the indoline 1 (table 1). The mechanism of the anaerobic part of these photoreactions were investigated by CIDNP experiments. It is possible to convert directly indoline 1 to the indolenine 2 , in 33% yield, by irradiation at 60° in the presence of oxygen.     

Synthesis,Structural Characterization and Photodecarbonylation Study of a Dicarbonyl Ruthenium(II)-Bisquinoline Complex

A photoactivatable ruthenium(II) carbonyl complex mer,cis-[Ru(II)Cl(BisQ)(CO)₂]PF₆ 2 was prepared using a tridentate bisquinoline ligand (BisQ=(2,6-diquinolin-2-yl)pyridin). Compound 2 was thoroughly characterized by standard analytical methods and single crystal X-ray diffraction. The crystal structure of the complex cation reveals a distorted octahedral geometry. The decarbonylation upon exposure to 350 and 420 nm light was monitored by UV/VIS absorbance and Fourier transform infrared spectroscopies in acetonitrile and 1 % (v/v) DMSO in water, respectively. The kinetic of the photodecarbonylation has been elucidated by multivariate curve resolution alternating least-squares analysis. The stepwise decarbonylation follows a serial mechanism. The first decarbonylation occurs very quickly whereas the second decarbonylation step proceeds more slowly. Moreover, the second rate constant is lower in 1 % (v/v) DMSO in water than in acetonitrile. In comparison to 350 nm irradiation, exposure to 420 nm light in acetonitrile results in a lower second rate constant.     

Über die thermische,katalytische und photochemische Stickstoff-Eliminierung des 1-Diazo-3-(1-methylcyclopenta-2,4-dienyl)-2-propanons

The Thermal, Catalytic, and Photochemical Denitrogenation of 1-Diazo-3-(1-methylcyclopenta-2,4-dienyl)-2-propanone The synthesis of the title compound 12 is described. This diazoketone, distinguished by its C_s-symmetry and by a built-in cisoid diene unit, gives 5-methyltricyclo[3.3.0.0^2,8]oct-6-ene-3-one ( 13 ) when subjected to thermal or catalytic denitrogenation with rhodium (II) acetate or copper (II) acetylacetonate. Direct irradiation of 12 at 350 nm causes Wolff rearrangement, whereas the benzophenone-sensitized photolysis gives again ketone 13 . A 1,4-carbene or carbenoid addition was never observed under the conditions described. The ketone 13 equilibrates thermally or under base catalysis with 1-methyltricyclo[3.3.0.0^2,8]oct-6-ene-3-one ( 17 ). The key step of this apparent CH₃ migration is shown to be a Cope rearrangement of the corresponding enols (hydroxysemibullvalenes).